One type of atmospheric re-entry vehicle (RV) is a ballistic RV which, after an initial launch and boost phase, follows a substantially purely ballistic path after separation from a launch vehicle. That is, the position of the RV target can be predetermined if the velocity of the RV and if the boost phase trajectory is known. One disadvantage associated with a purely ballistic RV is that, inasmuch as the target position can be predetermined after separation, interception of the RV can be readily accomplished.
To improve survivability, it is thus desirable to provide an improved type of RV which is an evader maneuvering RV (EMRV) capable of executing in-flight evasive maneuvering operations after re-entry. Inasmuch as the trajectory of the EMRV after re-entry would not be required to be purely ballistic, the position of the EMRV's target would remain uncertain until the completion of the maneuverers. Thus, interception of the EMRV would be made difficult to accomplish.
Such an EMRV would include a suitable maneuvering capability and also a three-axes navigation system for guidance. Preferably, the navigation system would employ a strap-down inertial navigator having ring laser gyroscopes (RLGs) which are inherently more rugged and capable of executing high-G maneuvers than are conventional mechanical gyroscopes. One purpose of the navigation system is to maintain EMRV position information during evasive maneuvering such that the EMRV can be guided to a target at the completion of maneuvers. The EMRV would also typically include an altitude measuring system, such as a radar altimeter, in order to fuse the EMRV's ordinance at a predetermined altitude.
Following the boost phase, and during a coast phase, the EMRV is spin stabilized. As can be appreciated, even with the greatly improved scale factor stability which is obtainable with modern RLGs, a high-G EMRV maneuvering phase will result in a significant EMRV position error at the completion of maneuvering due to the loss of altitude reference during the spin stabilized coast phase. If uncorrected, the computed position of the target relative to the EMRV will also be in error. Known techniques of compensating for the altitude reference error prior to high-G maneuver, or alternatively for the position error following the high-G maneuver are generally inappropriate in an EMRV due to at least the increased weight and complexity associated with such correction systems.
It is therefore one object of the invention to provide a three-axes position and a velocity correction to an inertial navigator.
It is another object of the invention to provide an EMRV with a three-axes position and a velocity correction at the completion of a maneuvering phase in order that the EMRV can be accurately guided to a desired location.
It is another object of the invention to provide an EMRV with a three-axes position and a velocity correction which does not require an appreciable increase in either the weight or complexity of the EMRV and which furthermore may be accomplished in a relatively brief interval of time.
It is one more object of the invention to provide an EMRV with a three-axes position and a velocity correction which does not require an appreciable increase in either the weight or complexity of the EMRV and which furthermore may be accomplished in a relatively brief interval of time by making an altitude measurement and processing the measurement to determine position and velocity corrections.